Refrigeration system including high pressure protection



Jan. 9, 1968 v G. L. MEAGHER 3,362,188

REFRIGERATION SYSTEM INCLUDING HIGH PRESSURE PROTECTION Filed May 51, 196 6 INVENTOR. GEORGE. L.- MEAGHER ms ATTORNEY United States Patent 3,362,188 REFRIGERATION SYSTEM INCLUDING HIGH PRESSURE PROTECTION George L. Meagher, Tyler, Tex., assignor to General Electric Company, a corporation of New York Filed May 31, 1966, Ser. No. 553,978 2 Claims. (Cl. 62-505) The present invention relates to refrigeration systems of either the cooling only or reversible type and is more particularly concerned with a refrigeration system including improved control means for limiting abnormally high side refrigerant pressure conditions.

Refrigeration systems, such as those employed for air conditioning, comprise in closed, series-flow connection a hermetic compressor, a first heat exchanger operating as a condenser flow control means and a second heat exchanger operating as an evaporator. The flow control means between the two heat exchangers may be either a fixed flow restrictor, such as capillary tube, or an expansion valve responsive, for example, to changes in low side or evaporator temperature or pressure. Fan means are normally also provided for circulating outdoor air over one heat exchanger and indoor air over the other heat exchanger. The compressor is driven by a driving motor and the power supply circuit for the motor normally includes a temperature responsive motor overload protector adapted to open the circuit upon an abnormal increase in the current flowing to the motor, an abnormal increase in the motor temperature or both. Many air cond-itioning refrigeration systems also include pressure limiting controls such as a high pressure cut out switch in the high or condenser side of the system to limit the maximum pressures that may be attained under poor condenser cooling conditions such as those resulting from condenser fan motor failure or other interruption of the air flow over the condenser.

It is an object of the present invention to provide improved high pressure protection means for a refrigeration system which does not require the use of a high pressure cut out switch.

A more specific object of the invention is to provide a refrigeration system including a hermetic compressor and means operable upon an abnormal differential between the high and low side pressures of the system for conducting hot high side refrigerant into the heating relationship with the usual motor overload protecting means whereby the protector will operate to limit the high pressure condition.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming part of the specification.

The sole figure of the drawing illustrates a reversible heat pump.

In accordance with one embodiment of the present invention, there is provided a refrigeration system comprising a hermetic compressor, a discharge line, a condenser, a flow control means, an evaporator and a suction line connected in a closed refrigerant circuit. An electric motor for driving the compressor is in the path of, and normally cooled by, low pressure refrigerant flowing to the compressor from the suction line. The power supply circuit for energizing the motor includes a motor overload protector in heat exchange with the motor and operable for opening the circuit upon a substantial increase in motor temperature as sensed by the protector. In order to limit the maximum pressures which may be attained in the high side or condenser portion of the system, the system includes a bypass including a normally closed pressure operated valve connecting the compressor discharge line with the suction line. This valve is adapted to be opened by an abnormal differential between the-refrigerant pressures in the high and low pressure sides of the system to provide a flow of hot compressed refrigerant over the motor so that the resultant warming of the overload protector will open the motor supply circuit.

The heat pump embodiment of the invention illustrated in the drawing comprises a hermetic compressor unit 1, a first or outdoor heat exchanger 2, flow control means in the form of a capillary tube 3, a second or indoor heat exchanger 4 and a reversing valve 5 whereby through suitable conduits, the compressor unit 1 can be connected in closed series flow relationship with the two heat exchangers so that the outdoor heat exchanger 2 functions either as a condenser or as an evaporator and the indoor heat exchanger 4 as either an evaporator or condenser.

The hermetic compressor unit 1 includes a compressor 6 driven by a motor 7, both of which are contained within a hermetic casing 8. A suction line 10 connecting the reversing valve with the compressor unit 1 has an outlet 11 extending through the casing above the motor 7 so that low pressure refrigerant entering the casing flows into heat exchange relationship with the motor. Compressed refrigerant from the compressor is conducted through a discharge line 12 to the reversing valve 5. Upon energization of the motor 7 with the reversing valve set for cooling operation of the heat pump, the compressor 6 withdraws low pressure refrigerant from the interior of the casing 8 and discharges high pressure refrigerant through the discharge line 12 and the reversing valve 5 to the outdoor heat exchanger 2 which then fuctions as a condenser. The high pressure refrigerant condensed in the outdoor heat exchanger 2 flows through the pressure reducing and flow restricting means 3 to the indoor coil 4 functioning as an evaporator. Vaporized refrigerant withdrawn from the indoor coil 4 flows through the suction line 10 to the interior of the casing 8.

Electric power is supplied to the motor 7 from a power supply circuit including power supply lines 14 and 15 one of which includes a motor overload protector 16 connected in series with the motor 7. This motor overload protector, which may be of the bimetallic switch or thermostat type is positioned in heat exchange relationship with some of the windings 18 of the motor 7 so as to be responsive to the motor or winding temperatures and is designed to open the motor circuit upon either an increase in the flow of current to the motor or an increase in the motor temperature.

During operation of the heat pump, the heat exchanger functioning as a condenser is cooled by means of an air stream passed thereover usually by means of a fan (not shown). Under normal operating conditions, the condenser operates within the predetermined range of high pressure conditions while the heat exchanger functioning as the evaporator operates at a lower pressure condition. The motor overload protector 16 functions to de-energize the motor whenever the temperature sensed thereby becomes abnormally high.

Prior air conditioning refrigeration systems of this type have frequently included pressure limiting controls in the high side or condenser side of the system to limit the maximum pressures which may be attained therein under conditions such as condenser fan failure or abnormal decrease in air flow over the condenser. Frequently this type of protection has been accomplished by means of a pressure operated switch responsive to pressure conditions within the high side or condenser side of the system and adapted to interrupt the compressor motor circuit at some predetermined abnormal pressure.

In accordance with the present invention, a high pressure switch of this type is eliminated and the desired system pressure protection is obtained by a refrigerant flow and motor control circuitry so designed that upon an occurrence of the abnormally high pressure differential between the discharge line 12 and the suction line 10, but high pressure refrigerant will be bypassed into heat exchange relationship with the motor overload protector 16 thereby increasing the temperature sensed by this protector and effecting de-energization of the motor 7. More specifically, there is provided a bypass line 20 connecting the discharge line 12 to the suction line 10 adjacent its inlet 11 to the casing 8. This bypass line includes a pressure operated valve 21 including a valve member 22 normally closing an inlet port 23 under the biasing action of a spring 24. The spring 24 is designed to maintain the valve closed under all normal pressure differential conditions existing in the system and to permit it to open under abnormal pressure conditions. When opened, the valve 21 permits the flow of hot high pressure refrigerant from the discharge line into the suction line 10 and through the outlet 11 of the suction line 10 into direct heating relationship with the motor and preferably also in direct contact with the overload protector 16. The overload protector 16 is thereby warmed to a temperature such that it opens the power supply circuit to the motor whereby de-energization of the motor prevents further increase in the high side pressure.

In order to better understand the operation of the invention, it may be noted that upon condenser fan or air flow failure, there is little or no condensation taking place in the condenser component of the system due to the fact that it is operating at abnormally high temperatures. As a result primarily gaseous rather than liquid refrigerant is present at the inlet end of the normal flow control means 3 and the mass flow capacity thereof is very limited under these conditions. The resultant decreased flow of refrigerant through the flow control means causes the compressor to operate at relatively low suction pressures even though the head pressure has become excessive. Such a condition may not increase the power required to drive the compressor motor sufficiently to cause the motor overload protector 16 to operate to correct the system malfunction of this type within safe pressure limitations.

However, by providing in accordance with the present invention a pressure operated spring-loaded mechanical unloader valve 21 between the discharge 12 and the suction line 10, this bypass valve in conjunction with the motor overload protector 16 serves to limit the operation of the compressor under conditions of system faults that create excessive pressure differentials between the high and low pressure sides of the system. When the pressure differential across the compressor discharge and suction lines exceeds a predetermined safe value, the unloader valve opens and bleeds high pressure gas to the suction line thereby tending to limit the pressure differential that may be developed. The high temperature discharge gas which is bled directly into the suction line enters the compressor casing at a point at which it warms the motor and the overload protector 16 so that the temperature sensed by this protector 16 rapidly rises and at a predetermined value, the motor overload protector opens the motor supply circuit. After the compressor motor has cooled sufficiently, the overload protector will again reclose starting the compressor. If the system fault causing the excessive head pressure remains, the protective systern will continue to cycle the compressor within safe system pressure conditions.

In addition to the cost advantage resulting from the elimination of the usual high pressure cut out, the subject protection system employing a mechanical unloader valve offers certain other advantages such as the reduction of nuisance service calls which frequently result from high pressure cut out switch tripping due to short duration high pressure transients. This is accomplished due to the time delay provided between the actual operation of the valve 21 and the tripping by the overload protector 16 and by the automatic re-energization of the compressor once the motor overload protector has cooled following de-energization of the motor 7. Also, as the valve 21 is exterior of the hermetic casing, it may be serviced or replaced without opening the casing.

While there has been shown and described a particular embodiment of the invention, it is to be understood that it is not limited thereto and is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A refrigeration system comprising a compressor, a discharge line, a condenser, flow control means, an evaporator and a suction line connected in closed refrigerant flow circuit;

an electric motor for driving said compressor and means for directing low pressure refrigerant from said suction line in heat exchange relationship with said motor,

a power supply circuit for energizing said motor and including a thermal overload protector positioned in heat exchange relationship with said motor for opening said circuit upon the sensing a predetermined abnormally high temperature,

said protector being positioned in the path of the flow of refrigerant from said suction line,

a bypass line including a normally closed unloader valve connecting said discharge and suction lines,

said valve opening upon an abnormal pressure differential between said discharge and suction lines to permit the flow of hot refrigerant from said discharge line to said suction line and into heat exchange relation with said motor to operate said protector and thereby de-energize said motor.

2. A refrigeration system comprising a hermetic compressor unit, a discharge line, a condenser, flow control means, an evaporator and a suction line connected in closed refrigerant flow circuit,

said compressor unit comprising a sealed casing having an inlet for receiving low pressure refrigerant from said suction line, a compressor and an electric motor for driving said compressor contained within said casing, said compressor withdrawing low pressure refrigerant from said casing and discharging hot compressed refrigerant to said discharge line,

a power supply circuit for energizing said motor and including a thermal overload protector positioned in heat exchange relationship with said motor and operable to interrupt the supply of current to said motor upon sensing a predetermined abnormally high motor temperature,

a bypass line including a normally closed unloader valve connecting said discharge and suction lines,

said valve opening upon an abnormal pressure differential between said discharge and suction lines to permit the flow of hot refrigerant from said discharge line to said suction line and into heat exchange relation with said motor to operate said protector and thereby de-energize said motor.

References Cited UNITED STATES PATENTS 2,963,878 12/1960 Beggs et al. 62-196 3,212,284 10/1965 Henderson 62-117 3,222,555 12/1965 Snoberger et al. 62-505 ROBERT A. OLEARY, Primary Examiner. 

1. A REFRIGERATION SYSTEM COMPRISING A COMPRESSOR, A DISCHARGE LINE, A CONDENSER, FLOW CONTROL MEANS, AN EVAPORATOR AND A SUCTION LINE CONNECTED IN CLOSED REFRIGERANT FLOW CIRCUIT; AN ELECTRIC MOTOR FOR DRIVING SAID COMPRESSOR AND MEANS FOR DIRECTING LOW PRESSURE REFRIGERATION FROM SAID SUCTION LINE IN HEAT EXCHANGE RELATIONSHIP WITH SAID MOTOR, A POWER SUPPLY CIRCUIT FOR ENERGIZING SAID MOTOR AND INCLUDING A THERMAL OVERLOAD PROTECTOR POSITIONED IN HEAT EXCHANGE RELATIONSHIP WITH SAID MOTOR FOR OPENING SAID CIRCUIT UPON THE SENSING A PREDETERMINED ABNORMALLY HIGH TEMPERATURE, A BYPASS LINE INCLUDING A NORMALLY CLOSED UNLOADER OF REFRIGERANT FROM SAID SUCTION LINE, A BYPASS LINE INCLUDING A NORMALLY CLOSED UNLOADER VALVE CONNECTING SAID DISCHARGE AND SUCTION LINES, SAID VALVE OPENING UPON AN ABNORMAL PRESSURE DIFFERENTIAL BETWEEN SAID DISCHARGE AND SUCTION LINES TO PERMIT THE FLOW OF HOT REFRIGERANT FROM SAID DISCHARGE LINE TO SAID SUCTION LINE AND INTO HEAT EXCHANGE RELATION WITH SAID MOTOR TO OPERATE SAID PROTECTOR AND THEREBY DE-ENERGIZE SAID MOTOR. 